The present invention relates to a gas flow-through line with sound absorption effect. The invention relates in particular to air flow-through pipelines with sound absorption effect.
As a possibility for sound absorption there are known so-called Helmholz absorbers, which however in dependence upon their geometric configuration, exhibit a good absorption effect only for narrowly restricted frequency ranges. Further, Helmholz absorbers usually have relatively large dimensions, which strongly restricts their field of application.
Further, there are known sound absorption devices of fibrous and porous materials, which however manifest a number of disadvantages. On the one hand, the frequently heterogeneous mixture of materials of these systems is recycling unfriendly. Furthermore, particles can detach themselves out of these materials, so that the systems are not suitable for lines carrying air. Moreover, the porous materials suffer from the fact that they manifest a strong take-up of water.
As a further possibility for sound absorption there are known so-called microperforated sheet absorbers, arranged in front of a rigid, i.e. reverberant, wall. The physical background of this kind of sound absorber is described in IBP-Mitteilung 261-21 (1994), xe2x80x9cNeue Forschungsergebnissexe2x80x94kurzgefaxcex2txe2x80x9d, of the Fraunhofer Institute for Structural Physics. The absorption effect with these absorbers is based in substance upon the viscous friction, which for example through-flowing air in the holes of the microperforation has to overcome.
From DE 4315759 C1 there is known a sound absorbing glass or transparent plastics component which has through-holes with a very small diameter in the range from 0.2 to 2 mm and which is mounted with a spacing in front of a rigid back wall. The sound absorbing component is provided in the manner of the plate with various shapings, such as for example concave or convex with reference to the back wall, or also in the shape of a roof. The advantage of these elements consists inter alia in that they are transparent and can also be employed in rooms subject to damp or moisture. Further, they can themselves represent design elements for a variety of rooms.
The microperforated absorbers known from the state of the art have the disadvantage that they must be employed as relatively large area plates at a spacing from a rigid back wall and thus are not suitable to follow complicated contours. Furthermore, the space requirement of the overall arrangement is increased.
It is thus the object of the present invention to provide a sound absorption arrangement which has a lesser requirement for space.
In accordance with the present invention there is thus provided a gas flow-through line with a sound absorption effect, whereby the wall of the line contains through-going microperforations. As microperforations there are to be understood holes with a diameter of less than 1-2 mm.
The line may in particular be a pipeline carrying a flow of air, having a substantially circular cross-section.
The free hole surface of the microperforations takes up preferably a maximum of 10 per cent of the total surface of the wall of the line.
Preferably, the microperforations have approximately circular through-going holes having a diameter of the order of 0.40 to 0.50 mm, in particular about 0.45 mm.
The microperforations may have any arbitrary geometry, and may also be slit-shaped.
The line may have second holes, the free diameter of which is substantially larger than that of the microperforations, but smaller than about 5 mm.
The line may be of a polymer plastics, rubber or rubber-like materials, or of natural products.
A line of the above-mentioned kind can find employment in particular as air suction hose of an internal combustion engine.
The line may also be employed as an air suction hose of a turbocharger of an internal combustion engine.
The line of the above mentioned kind can be employed for sound absorption of frequencies of more than 1,000 Hz.
A line having the second holes can be employed in particular for sound absorption of frequencies of more than 500 Hz. There may be provided also perforations which differ from section to section.
By means of an acoustically optimised sheathing of the line having the microperforations, at least in sections, the frequency band over which airborne noise is absorbed can be significantly widened. This sheathing may be effected in coffer-like sections.
Through forming the wall of the line by means of at least two perforated wall layer parts, which are displaceable with respect to one another, the effective opening surface of the perforations can be configured to be settable.
The present invention relates further to a method for the manufacture of the line of the above mentioned kind, whereby the method comprises the step of manufacturing the microperforations by means of stamping (and thus mechanically) and/or by means of working with a laser beam.